Electroflow method of electrocoating

ABSTRACT

A selected, electrically conductive surface area on a metal object, such as a scoreline, scratch, cutedge, etc., may be individually coated by a dipless electroflow method of electrocoating. In the electroflow method, the metal object is moved along a straight line path of travel. A freestanding stream of coating material is aligned with and impinged onto a selected, electrically conductive surface area of the moving metal object. Simultaneously, a direct current is maintained flowing within the coating stream, in the case of an anodic coating material, between a negatively charged source of the coating material and the selected, electrically conducted surface area of the positively charged moving metal object, to individually coat the selected, electrically conductive surface area of the moving metal object. In the case of a cathodic coating material, the source of the coating material is positively charged and the moving metal object is negatively charged.

United States Patent Landauer [451 Apr. 25, 1972 [54] ELECTROF LOW METHOD OF ELECTROCOATING [2]] App]. No.: 887,003

[52] U.S.Cl ..204/181 [51] Int. Cl. ..B0lk 5/02, C23b 13/00 [58] Field of Search ..204/181 [56] References Cited UNITED STATES PATENTS 6/1948 Schneider ..204/181 1/1968 Tanner..... ....204/18l 1/1970 Johnson ..204/181 Primary Examiner- Howard S. Williams Attorney-Robert P. Auber, George P. Ziehmer, Leonard R, Kohan and Kenneth H. Murray [5 7] ABSTRACT A selected, electrically conductive surface area on ametal object, such as a scoreline, scratch, cutedge, etc., may be individually coated by a dipless electroflow method of electrocoating. 1n the electroflow method, the metal object is moved along a straight line path of travel. A freestanding stream of coating material is aligned with and impinged onto a selected, electrically conductive surface area of the moving metal object. Simultaneously, a direct current is maintained flowing within the coating stream, in the case of an anodic coating material, between a negatively charged source of the coatingmaterial and the selected, electrically conducted surface area of the positively charged moving metal object, to individually coat the selected, electrically conductive surface area of the moving metal object. In the case of a cathodic coating material, the source of the coating material is positively charged and the moving metal object is negatively charged.

6 Claims, 6 Drawing Figures Patented April 25, 1972 3,658,677

- INVENTOR.

LEROY LANDAUER 61 63 Bglmwd W$ ATTORNEY ELECTROFLOW METHOD OF ELECTROCOATING BACKGROUND OF THE INVENTION The present invention relates broadly to a method of coating a metal object, and is more particularly directed to a novel electroflow method of electrocoating a selected, electrically conductive surface area of a metal object without dipping the whole metal object, or any part thereof, into a coating bath.

Electrocoating is the electrodeposition of resinous coating materials, such as paint materials,from water base solutions, suspensions or dispersions. In the case of anodic coating materials, the coating ions or particles carry a negative charge in the water base bath and these particles migrate to and discharge onto any positively charged metal which may be immersed into the coating bath. In the case of cathodic coating materials, the coating ions or particles carry a positive charge in the water base bath and these particles migrate to and discharge onto any negatively charged metal which may be immersed into the coating bath.

A layer of coating is electrodeposited on the electrically charged metal object, as the direct current flows between an oppositely, electrically charged wire or rod, immersed in the coating bath, and the metal object. The process is usually driven by an electrical potential in the range of 200 to 500 volts. The electrodeposition of coating can take place only on electrically conductive surface areas of the metal object because only such areas will allow the necessary flow of direct current.

The thickness of the electrodeposited coating layer is automatically regulated by a characteristically low electrical conductivity of the particular coating materials ordinarily used. In other words, depending on the particular coating material used, once a certain layer thickness of coating material has attached to the electrically conductive surface area of the metal object, the electrodeposited coating material, in having a low electrical conductivity characteristic, increasingly tends to insulate the surface area from the coating bath in which it is immersed, transforming it into a non-conductivesurface, whereby direct current flow therein greatly diminishes and eventually ceases, with the resulting inhibition of further electrodeposition of coating material.

One particular area where it has been found desirable to coat metal objects is in the metal can manufacturing field. It is necessary that all the exposed, uncoated surface areas on the metal can be coated to protect the metal from corrosion.

One method of perfecting the coverage of the coating on the metal can is to initially roller coat the surface area while in the flat coil or sheet form, next fabricate the can from coated metal plates which have been cut from the large sheets of material, and then spray coating on the surface area of the can to repair possible exposed, uncoated breaks in the roller coat due to the fabrication operation, such as raw cut edge surfaces produced on the otherwise coated metal plates when the plates were cut from the large sheets of material.

This spraying operation is frequently objectionable because of the solvents involved, the manufacturing difficulties inherent in high speed spraying operations, and the large amount of coating which must be sprayed in order to assure coverage of the relatively small uncoated surface areas of the metal can.

The conventional immersion method of electrodepositing coating material on the metal can involves several disadvantages which severely impair the practical use of this electrocoating process for coating cans.

A conventional method of electrodepositing a coating material onto an electrically conductive surface area of a metal object requires that the metal object be dipped or immersed into a coating bath. This need to immerse the metal object, even if only partially, into the coating bath in order to coat it constitutes a disadvantage in the use of this method in conjunction with high speed straight line manufacturing operations because the moving metal object must change direction in order to get into and out of a dip tank.

Another serious disadvantage of this conventional method is that usually the coating material cannot be limited so that it contacts only a selected surface area of the metal object. Instead, as is the norrnal case, the entire surface area of the metal object must be immersed or dipped into the coating bath in order for just a very small surface area thereof to be coated. The complete immersion of the metal object into the coating bath disadvantageously results in excessive bath dragout and a greater rinsing and cleaning (dragout removal) problems.

All of the above disadvantages associated with the spraying of cans or the electrocoating cans by the immersion method may be overcome by the use of a novel electroflow method of electrocoating a selected surface area of a metal object, for instance, the exposed, uncoated cut edge surface of a metal plate which otherwise has been roller. coated prior to its fabrication.

The present invention relates to a novel electroflow method of electrodepositing a coating material onto a metal object withoutrerouting the metal object from its normal straight line path of travel and mode of conveyance during or after other manufacturing operations. In other words, in the novel electroflow method of electrocoating forming the present invention, the metal object to be coated need not be brought to and then dipped into the coating bath, but, instead the electro coating operating is brought to the moving metal object. Further, even though the need for immersing the metal object into a coating bath has been eliminated, a specific or selected electrically conductive surface area of the moving metal object can still be coated, without any dragout, rinsing or cleaning problems resulting therefrom.

SUMMARY OF THE INVENTION The novel electroflow method of electrocoating a metal object forming the present invention comprises moving a metal object, having a selected electrically conductive surface area to be coated,along a straight line path of travel and impinging a freestanding stream of coating material onto the selected electrically conductive surface area of the moving metal object, while maintaining a direct current flowing in the freestanding stream such that coating material is electrodeposited onto the selected electrically conductive surface area of the moving metal object.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration depicting a preferred or exemplary electrocoating arrangement which operates according to the novel electroflow method forming the present invention; and

FIGS. 2-are schematic illustrations depicting several other electrocoating arrangements which also operate according to the novel electroflow method forming the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preferred or exemplary embodiment of the instant invention, FIG. 1 shows a metal object, generally designated 20, being moved by a suitable conveying means (not shown) along a substantially straight line path of travel (in the direction of the large arrow as shown). The metal object 20 has an electrically conductive surface area, generally designated 22, which has been selected for coating, and which, for purposes of clarity, may be in the form of an exposed, uncoated metal plate cutedge. One or more bubblers 24 are aligned in such a position that, relative to the straight line path of travel of the moving metal object 20, a fountain-like, freestanding stream 26 of coating material flowing from the bubblers 24 will impinge onto the selected electrically conductive surface area 22 of the moving metal object 20. The freestanding stream 26 of coating material has substantially laminar flow characteristics, as opposed to turbulent flow characteristics.

At the same time that the freestanding stream 26 of coating material impinges onto the selected surface area 22 of the moving metal object 20, a direct electrical current is maintained within the freestanding stream 26 of coating material, in the case of an anodic coating material, flowing between a negatively charged, metallic bubbler nozzle 28, or some other negatively charged electrode (not shown) which may be inserted within the freestanding stream 26 of coating material, and the selected surface area 22 of the moving metal object which is positively charged, i.e., through a ground. in the case of a cathodic coating material, the metallic bubbler nozzle 28 would be positively charged and the moving metal object would be negatively charged.

The direct electrical current flowing within the freestanding stream 26 of coating material causes coating material to electrodepositonto the selected surface area 22, which is the area impinged by the freestanding stream 26. Coating material furnished by some suitable means (not shown) may be continuously supplied to the bubblers 24 via an outlet 30. Any residualcoating material, in excess of the amount which electrodeposits onto the selected surface area 22 of the moving metal object 20, may be drained away via an outlet 32 in a collection reservoir 34..

Even though residual coating material, prior to being drained away, may erratically flow onto and wet electrically conductive surface areas which are remote from surface area 22 which was selected for electrocoating, the electrodeposition of coating material will occur only at the surface area which is directly in the linear path of laminar stream flow or immediately adjacent thereto, because conventional coating materials characteristically have low throwing power, i.e., have almost no independent capability of conducting direct electric current to remote, wetted electrically conductive surface areas in order to coat such areas. In other words, while residual coating material may erratically flow onto remote, electrically conductive I surface areas, such erratic flow of residual coating will not support and carry with it sufficient direct electric current flow for electrocoating to occur at such remote surfaceareas. lt maybe said that thepath of the direct electric current flowing in the freestanding stream 26 does not turn the corner" with the coating stream flow, but instead terminates, upon impingement of. the stream 26 onto the selected electrically conductive surface'22 of the electrically charged moving metal object20.

An edge 36 of the selected surface area 22 of the moving metal object 20 shown on the right side of the bubblers 24 is no longer electrically conductive now having a coating thereon. An edge 38 of the selected surface area 22 of the moving metal object 20 shown on the left side of the bubblers 24 is electrically conductive and yet to be coated.

In the modified electrocoating arrangements illustrated by FIGS. 26,.the parts of the set-ups which are identical to those described above in connection with FIG. 1 have been given the same reference numbers and will not be described again.

In one modified electrocoating arrangement, FIG. 2 shows a hopper 40 aligned such that, relative to the straight line path of travel of the moving metal object 20, a curtain-like, freestanding stream 46 of coating material, emitted from a bottom slot 44 in the hopper 40, will impinge onto the selected electrically conductive surface area 22 of the moving metal object 20. At the same time that the curtain-like stream 46 of coating material impinges onto the selected surface area 22 of the moving metal object 20, a direct current is maintained within the curtain-like stream 46 of coating material, flowing between a negatively charged electrode strip 48, or some other negatively charged electrode (not shown) which may be inserted within the stream 46 of coating material, and the selected surface area 22 of the moving metal object 20 which is positively charged through a ground. The direct current flowing within the curtain-like stream 46 of coating material causes coating material to electrodeposit onto the selected surface area 22 of the moving metal object 20. Coating material furnished by some suitable means (not shown) may be continuously supplied to the hopper 40 via an inlet 50. Any residual coating material, in excess of the amount which electrodeposits onto the selected surface area 22 of the moving metal object 20, may be drained away via an outlet 52 in a collection reservoir 54.

In another electrocoating arrangement, FIG. 3 shows a coating material reservoir 56 aligned such that, relative to the straight line path of travel of the moving metal object 20, a curtain-like, freestanding stream 58 of coating material, poured from an overflow 60 in the reservoir 56, will impinge onto the selected electrically conductive surface area 22 of the moving metal object 20. At the same time that the curtainlike stream 58 of coating material impinges onto the selected surface area 22 of the moving metal object 20, a direct current is maintained within the curtain-like stream 58 of coating material, flowing between a negatively charged electrode strip 62, or some other negatively charged electrode which may be inserted within the stream 58 of coating material (not shown), and the selected surface area 22 of the moving metal object 20 which is positively charged through a ground. The direct current flowing within the curtain-like stream 58 of coating material causes coating material to electrodeposit onto the selected surface area 22 of the moving metal object 20.

Coating material furnished by a suitable means (not shown) may be continuously supplied to reservoir 56 via an inlet 59. Any residual coating material in excess of the amount which electrodeposits onto the selected surface area 22 of the moving metal object 20, may be drained away via an outlet 61 in a collection reservoir 63.

In still another electrocoating arrangement, FIG. 4 the freestanding puddle 72 of an inlet tube 64 which pours a freestanding stream 66 of coating material onto the center of a non-conductive table 68, whereupon the coating material spreads out and continuously runsoff the table edges 70 such that a continuously flowing, freestanding puddle 72 of coating material is formed on the non-conductive table 68. The nonconductive table 68 is aligned such that, relative to the straight line path of travel of the moving metal object 20, the selected electrically conductive surface area 22 of the moving metal object 20 contacts the continuously flowing, freestanding puddle 72 of coating material. At the same time. that the freestanding puddle 72 of coating material impinges onto the selected surface area 22 of the moving metal object 20, a direct current is maintained within the freestanding puddle 72 of coating material, flowing between a negatively charged electrode strip 74, or some other negatively charged electrode which may be inserted within the puddle 72 of coating material (not shown), and the selected surface area 22 of the moving metal object 20 which is positively charged through a ground. The direct'current flowing within the freestanding puddle 72 of coating material causes coating material to electrodeposit onto the selected surface area 22 of the moving metal object 20.

Coating material furnished by a suitable means (not shown) may be continuously supplied to inlet tube 64 via an inlet 71. Any residual coating material, in excess of the amount which electrodeposits onto the selected surface area 22 of the moving metal object 20, may be drained away via outlet 73 in a collection reservoir 75.

In a further amplification of the electrocoating arrangement, FIG. 5 shows a non-conductive wheel 76 partially submerged in a coating material reservoir 77. The wheel 76 is continuously rotated by a suitable means (not shown) to provide a continuously flowing, freestanding film 78 of coating material on the non-conductive wheel surface 80. The wheel 76 is aligned such that, relative to the straight line path of travel of the moving metal object 20, the selected electrically conductive surface area 22 of the moving metal object 20 contacts the continuously flowing, freestanding film 78 of coating material. At the same time that the freestanding film 78 of coating material impinges onto the selected surface area 22 of the moving metal object 20, a direct current is maintained within the freestanding film 78 of coating material, flowing between a negatively charged electrode strip 82, or some other negatively charged electrode which may be inserted within the film 78 of coating material (not shown), and the selected surface area 22 of the moving metal object which is positively charged through a ground. The direct current flowing within the freestanding film 78 of coating material causes coating material to electrodeposit onto the selected surface area 22 of the moving metal object 20. Coating material furnished by some suitable means (not shown) may be continuously supplied to the coating material reservoir 77 via an inlet 86 and drained therefrom via an outlet 88.

In yet another electrocoating arrangement, FIG. 6 illustrates a nozzle 90 aligned such that, relative to the straight line path of travel of the moving metal object 20, a freestanding stream 92 of coating material, emitted downwardly from the nozzle 90, will impinge onto the selected electrically conductive surface area 22 of the moving metal object 20. At the same time that the stream 92 of coating material impinges onto the selected surface area 22 of the moving metal object 20, a direct current is maintained within the stream 92 of coating material, flowing between a negatively charged nozzle electrode 94, or some other negatively charged electrode which may be inserted within the stream 92 of coating material (not shown), and the selected surface area 22 of the moving metal object 20 which is positively charged through a ground. The direct current flowing within the freestanding stream 92 of coating material causes coating material to electrodeposit onto the selected surface area 22 of the moving metal object 20. Coating material furnished by some suitable means (not shown) may be continuously supplied to the nozzle 90 via an inlet 96. Any residual coating material, in excess of the amount which electrodeposits onto the selected surface area 22 of the moving metal object 20, may be drained away via an outlet 98 in a collection reservoir 100.

it is thought that the invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement of the steps of the method without departing from the spirit and scope of the invention or sacrificing allof its material advantages, the form hereinbefore described being merely a preferred or exemplary embodiment thereof.

lclaim:

1. An electroflow method of electrocoating a selected electrically conductive surface area of a metal object, comprising the steps of:

bubbling a fountain-like, freestanding stream of coating material upwardly onto the selected electrically conductive surface area of the metal object; and

simultaneously maintaining a direct electrical current flowing within said freestanding stream of coating material such that the coating material electrodeposits onto the selected electrically conductive surface area of the metal object.

2. An electroflow method of electrocoating a selected electrically conductive surface'area of a metal object, comprising the steps of:

bubbling a fountain-like, freestanding stream of coating material upwardly;

moving the metal object along a substantially straight line path of travel such that the selected electrically conductive surface area of the metal object contacts the uppermost portion of the bubbling stream of coating material; and simultaneously maintaining a direct electrical current flowing within said freestanding bubbling stream of coating material such that the coating material electrodeposits onto the selected electrically conductive surface area of the moving metal object. 3. An electroflow method of electrocoating a selected electrically conductive surface area of a metal object, comprising the ste s of: p

rota mg a non-conductive wheel partially submerged in a coating material reservoir to provide a continuously flowing film of coating material on the surface of said wheel in contact with the selected electrically conductive surface area of the metal object; and

simultaneously maintaining a direct electrical current flowing within said film of coating material such that the coating material electrodeposits onto the selected electrically conductive surface area of the metal object. 4. An electroflow method of electrocoating a selected electrically conductive surface area of a metal object, comprising the steps'of:

rotating a non-conductive wheel partially submerged in a coating material reservoir to provide a continuously flowing film of coating material on the surface of said wheel;

moving the metal object along a substantially straight line path of travel such that the selected electrically conductive surface area of the metal object contacts the flowing film of coating material; and simultaneously maintaining a direct electrical current flowing within said flowing film of coating material such that the coating material electrodeposits onto the selected electrically conductive surface area of the moving metal object. 5. An electroflow method of electrocoating a selected electrically conductive surface area of a metal object, comprising the steps of:

pouring a stream of coating material onto a non-conductive horizontal surface to form a continuously flowing puddle of coating material in contact with the selected electrically conductive surface area of the metal object; and

simultaneously maintaining a direct electrical current flowing within said puddle of coating material such that the coating material electrodeposits onto the selected electrically conductive surface area of the metal object.

6. An electroflow method of electrocoating a selected electrically conductive surface area of a metal object, comprising the steps of:

. pouring a stream of coating material onto a non-conductive horizontal surface to form a continuously flowing puddle of coating material; moving the metal object along a substantially straight line path of travel such that the selected electrically conductive surface area of the metal object contacts the freestanding, flowing puddle of coating material; and simultaneously maintaininga direct electrical current flowing within said puddle of coating material such that the coating material electrodeposits onto the selected electrically conductive surface area of the metal object. 

2. An electroflow method of electrocoating a selected electrically conductive surface area of a metal object, comprising the steps of: bubbling a fountain-like, freestanding stream of coating material upwardly; moving the metal object along a substantially straight line path of travel such that the selected electrically conductive surface area of the metal object contacts the uppermost portion of the bubbling stream of coating material; and simultaneously maintaining a direct electrical current flowing within said freestanding bubbling stream of coating material such that the coating material electrodeposits onto the selected electrically conductive surface area of the moving metal object.
 3. An electroflow method of electrocoating a selected electrically conductive surface area of a metal object, comprising the steps of: rotating a non-conductive wheel partially submerged in a coating material reservoir to provide a continuously flowing film of coating material on the surface of said wheel in contact with the selected electrically conductive surface area of the metal object; and simultaneously maintaining a direct electrical current flowing within said film of coating material such that the coating material electrodeposits onto the selected electrically conductive surface area of the metal object.
 4. An electroflow method of electrocoating a selected electrically conductive surface area of a metal object, comprising the steps of: rotating a non-conductive wheel partially submerged in a coating material reservoir to provide a continuously flowing film of coating material on the surface of said wheel; moving the metal object along a substantially straight line path of travel such that the selected electrically conductive surface area of the metal object contacts the flowing film of coating material; and simultaneously maintaining a direct electrical current flowing within said flowing film of coating material such that the coating material electrodeposits onto the selected electrically conductive surface area of the moving metal object.
 5. An electroflow method of electrocoating a selected electrically conductive surface area of a metal object, comprising the steps of: pouring a stream of coating material onto a non-conductive horizontal surface to form a continuously flowing puddle of coating material in contact with the selected electrically conductive surface area of the metal object; and simultaneously maintaining a direct electrical current flowing within said puddle of coating material such that the coating material electrodeposits onto the selected electrically conductive surface area of the metal object.
 6. An electroflow method of electrocoating a selected electrically conductive surface area of a metal object, comprising the steps of: pouring a stream of coating material onto a non-conductive horizontal surface to form a continuously flowing puddle of coating material; moving the metal object along a substantiaLly straight line path of travel such that the selected electrically conductive surface area of the metal object contacts the freestanding, flowing puddle of coating material; and simultaneously maintaining a direct electrical current flowing within said puddle of coating material such that the coating material electrodeposits onto the selected electrically conductive surface area of the metal object. 